# ntpd: Network Time Protocol (NTP) Daemon User’s Manual

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# ntpd: Network Time Protocol (NTP) Daemon User Manual

The `ntpd` program is an operating system daemon that synchronizes the system clock to remote NTP time servers or local reference clocks. It is a complete implementation of NTP version 4 defined by RFC-5905, but also retains compatible with version 3 defined by RFC-1305 and versions 1 and 2, defined by RFC-1059 and RFC-1119, respectively. The program can operate in any of several modes, including client/server, symmetric and broadcast modes, and with both symmetric-key and public-key cryptography.

This document applies to version 4.2.8p15 of `ntpd`.

## Short Table of Contents

- 1 Description

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## 1 Description

The `ntpd` program ordinarily requires a configuration file described at ‘ntp.conf’. This configuration file contains configuration commands described on the pages listed above. However a client can discover remote servers and configure them automatically. This makes it possible to deploy a fleet of workstations without specifying configuration details specific to the local environment.

The `ntpd` program normally operates continuously while adjusting the system time and frequency, but in some cases this might not be practical. With the `-q` option `ntpd` operates as in continuous mode, but exits just after setting the clock for the first time. Most applications will probably want to specify the `iburst` option with the `server` command. With this option an initial volley of messages is exchanged to groom the data and set the clock in about ten seconds’ time. If nothing is heard after a few minutes’ time, the daemon times out and exits without setting the clock.

Next: Usage, Previous: ntpd Description, Up: ntpd Description

### 1.1 Invoking ntpd

The `ntpd` utility is an operating system daemon which sets and maintains the system time of day in synchronism with Internet standard time servers. It is a complete implementation of the Network Time Protocol (NTP) version 4, as defined by RFC-5905, but also retains compatibility with version 3, as defined by RFC-1305, and versions 1 and 2, as defined by RFC-1059 and RFC-1119, respectively.

The `ntpd` utility does most computations in 64-bit floating point arithmetic and does relatively clumsy 64-bit fixed point operations only when necessary to preserve the ultimate precision, about 232 picoseconds. While the ultimate precision is not achievable with ordinary workstations and networks of today, it may be required with future gigahertz CPU clocks and gigabit LANs.

Ordinarily, `ntpd` reads the `ntp.conf(5)` configuration file at startup time in order to determine the synchronization sources and operating modes. It is also possible to specify a working, although limited, configuration entirely on the command line, obviating the need for a configuration file. This may be particularly useful when the local host is to be configured as a broadcast/multicast client, with all peers being determined by listening to broadcasts at run time.

If NetInfo support is built into `ntpd` then `ntpd` will attempt to read its configuration from the NetInfo if the default `ntp.conf(5)` file cannot be read and no file is specified by the `-c` option.

Various internal `ntpd` variables can be displayed and configuration options altered while the `ntpd` is running using the `ntpq(1ntpqmdoc)` and `ntpdc(1ntpdcmdoc)` utility programs.

When `ntpd` starts it looks at the value of `umask(2)`, and if zero `ntpd` will set the `umask(2)` to 022.

This section was generated by AutoGen, using the `agtexi-cmd` template and the option descriptions for the `ntpd` program. This software is released under the NTP license, <http://ntp.org/license>.

Next: ntpd ipv4, Up: ntpd Invocation

#### 1.1.1 ntpd help/usage (`--help`)

This is the automatically generated usage text for ntpd.

The text printed is the same whether selected with the `help` option (`--help`) or the `more-help` option (`--more-help`). `more-help` will print the usage text by passing it through a pager program. `more-help` is disabled on platforms without a working `fork(2)` function. The `PAGER` environment variable is used to select the program, defaulting to `more`. Both will exit with a status code of 0.

    ntpd - NTP daemon program - Ver. 4.2.8p15
    Usage:  ntpd [ -<flag> [<val>] | --<name>[{=| }<val>] ]... \
                    [ <server1> ... <serverN> ]
      Flg Arg Option-Name    Description
       -4 no  ipv4           Force IPv4 DNS name resolution
                                    - prohibits the option 'ipv6'
       -6 no  ipv6           Force IPv6 DNS name resolution
                                    - prohibits the option 'ipv4'
       -a no  authreq        Require crypto authentication
                                    - prohibits the option 'authnoreq'
       -A no  authnoreq      Do not require crypto authentication
                                    - prohibits the option 'authreq'
       -b no  bcastsync      Allow us to sync to broadcast servers
       -c Str configfile     configuration file name
       -d no  debug-level    Increase debug verbosity level
                                    - may appear multiple times
       -D Num set-debug-level Set the debug verbosity level
                                    - may appear multiple times
       -f Str driftfile      frequency drift file name
       -g no  panicgate      Allow the first adjustment to be Big
                                    - may appear multiple times
       -G no  force-step-once Step any initial offset correction.
       -i --- jaildir        built without --enable-clockctl or --enable-linuxcaps or --enable-solarisprivs
       -I Str interface      Listen on an interface name or address
                                    - may appear multiple times
       -k Str keyfile        path to symmetric keys
       -l Str logfile        path to the log file
       -L no  novirtualips   Do not listen to virtual interfaces
       -n no  nofork         Do not fork
                                    - prohibits the option 'wait-sync'
       -N no  nice           Run at high priority
       -p Str pidfile        path to the PID file
       -P Num priority       Process priority
       -q no  quit           Set the time and quit
                                    - prohibits these options:
                                    saveconfigquit
                                    wait-sync
       -r Str propagationdelay Broadcast/propagation delay
          Str saveconfigquit Save parsed configuration and quit
                                    - prohibits these options:
                                    quit
                                    wait-sync
       -s Str statsdir       Statistics file location
       -t Str trustedkey     Trusted key number
                                    - may appear multiple times
       -u --- user           built without --enable-clockctl or --enable-linuxcaps or --enable-solarisprivs
       -U Num updateinterval interval in seconds between scans for new or dropped interfaces
          Str var            make ARG an ntp variable (RW)
                                    - may appear multiple times
          Str dvar           make ARG an ntp variable (RW|DEF)
                                    - may appear multiple times
       -w Num wait-sync      Seconds to wait for first clock sync
                                    - prohibits these options:
                                    nofork
                                    quit
                                    saveconfigquit
       -x no  slew           Slew up to 600 seconds
          opt version        output version information and exit
       -? no  help           display extended usage information and exit
       -! no  more-help      extended usage information passed thru pager

    Options are specified by doubled hyphens and their name or by a single
    hyphen and the flag character.

    The following option preset mechanisms are supported:
     - examining environment variables named NTPD_*

    Please send bug reports to:  <http://bugs.ntp.org, bugs@ntp.org>

Next: ntpd ipv6, Previous: ntpd usage, Up: ntpd Invocation

#### 1.1.2 ipv4 option (-4)

This is the “force ipv4 dns name resolution” option.

This option has some usage constraints. It:

- must not appear in combination with any of the following options: ipv6.

Force DNS resolution of following host names on the command line to the IPv4 namespace.

Next: ntpd authreq, Previous: ntpd ipv4, Up: ntpd Invocation

#### 1.1.3 ipv6 option (-6)

This is the “force ipv6 dns name resolution” option.

This option has some usage constraints. It:

- must not appear in combination with any of the following options: ipv4.

Force DNS resolution of following host names on the command line to the IPv6 namespace.

Next: ntpd authnoreq, Previous: ntpd ipv6, Up: ntpd Invocation

#### 1.1.4 authreq option (-a)

This is the “require crypto authentication” option.

This option has some usage constraints. It:

- must not appear in combination with any of the following options: authnoreq.

Require cryptographic authentication for broadcast client, multicast client and symmetric passive associations. This is the default.

Next: ntpd configfile, Previous: ntpd authreq, Up: ntpd Invocation

#### 1.1.5 authnoreq option (-A)

This is the “do not require crypto authentication” option.

This option has some usage constraints. It:

- must not appear in combination with any of the following options: authreq.

Do not require cryptographic authentication for broadcast client, multicast client and symmetric passive associations. This is almost never a good idea.

Next: ntpd driftfile, Previous: ntpd authnoreq, Up: ntpd Invocation

#### 1.1.6 configfile option (-c)

This is the “configuration file name” option. This option takes a string argument. The name and path of the configuration file, `/etc/ntp.conf` by default.

Next: ntpd panicgate, Previous: ntpd configfile, Up: ntpd Invocation

#### 1.1.7 driftfile option (-f)

This is the “frequency drift file name” option. This option takes a string argument. The name and path of the frequency file, `/etc/ntp.drift` by default. This is the same operation as the `driftfile` `driftfile` configuration specification in the `/etc/ntp.conf` file.

Next: ntpd force-step-once, Previous: ntpd driftfile, Up: ntpd Invocation

#### 1.1.8 panicgate option (-g)

This is the “allow the first adjustment to be big” option.

This option has some usage constraints. It:

- may appear an unlimited number of times.

Normally, `ntpd` exits with a message to the system log if the offset exceeds the panic threshold, which is 1000 s by default. This option allows the time to be set to any value without restriction; however, this can happen only once. If the threshold is exceeded after that, `ntpd` will exit with a message to the system log. This option can be used with the `-q` and `-x` options. See the `tinker` configuration file directive for other options.

Next: ntpd jaildir, Previous: ntpd panicgate, Up: ntpd Invocation

#### 1.1.9 force-step-once option (-G)

This is the “step any initial offset correction.” option. Normally, `ntpd` steps the time if the time offset exceeds the step threshold, which is 128 ms by default, and otherwise slews the time. This option forces the initial offset correction to be stepped, so the highest time accuracy can be achieved quickly. However, this may also cause the time to be stepped back so this option must not be used if applications requiring monotonic time are running. See the `tinker` configuration file directive for other options.

Next: ntpd interface, Previous: ntpd force-step-once, Up: ntpd Invocation

#### 1.1.10 jaildir option (-i)

This is the “jail directory” option. This option takes a string argument.

This option has some usage constraints. It:

- must be compiled in by defining `HAVE_DROPROOT` during the compilation.

Chroot the server to the directory `jaildir` . This option also implies that the server attempts to drop root privileges at startup. You may need to also specify a `-u` option. This option is only available if the OS supports adjusting the clock without full root privileges. This option is supported under NetBSD (configure with `--enable-clockctl`) or Linux (configure with `--enable-linuxcaps`) or Solaris (configure with `--enable-solarisprivs`).

Next: ntpd keyfile, Previous: ntpd jaildir, Up: ntpd Invocation

#### 1.1.11 interface option (-I)

This is the “listen on an interface name or address” option. This option takes a string argument `iface`.

This option has some usage constraints. It:

- may appear an unlimited number of times.

Open the network address given, or all the addresses associated with the given interface name. This option may appear multiple times. This option also implies not opening other addresses, except wildcard and localhost. This option is deprecated. Please consider using the configuration file `interface` command, which is more versatile.

Next: ntpd logfile, Previous: ntpd interface, Up: ntpd Invocation

#### 1.1.12 keyfile option (-k)

This is the “path to symmetric keys” option. This option takes a string argument. Specify the name and path of the symmetric key file. `/etc/ntp.keys` is the default. This is the same operation as the `keys` `keyfile` configuration file directive.

Next: ntpd novirtualips, Previous: ntpd keyfile, Up: ntpd Invocation

#### 1.1.13 logfile option (-l)

This is the “path to the log file” option. This option takes a string argument. Specify the name and path of the log file. The default is the system log file. This is the same operation as the `logfile` `logfile` configuration file directive.

Next: ntpd modifymmtimer, Previous: ntpd logfile, Up: ntpd Invocation

#### 1.1.14 novirtualips option (-L)

This is the “do not listen to virtual interfaces” option. Do not listen to virtual interfaces, defined as those with names containing a colon. This option is deprecated. Please consider using the configuration file `interface` command, which is more versatile.

Next: ntpd nice, Previous: ntpd novirtualips, Up: ntpd Invocation

#### 1.1.15 modifymmtimer option (-M)

This is the “modify multimedia timer (windows only)” option.

This option has some usage constraints. It:

- must be compiled in by defining `SYS_WINNT` during the compilation.

Set the Windows Multimedia Timer to highest resolution. This ensures the resolution does not change while ntpd is running, avoiding timekeeping glitches associated with changes.

Next: ntpd pidfile, Previous: ntpd modifymmtimer, Up: ntpd Invocation

#### 1.1.16 nice option (-N)

This is the “run at high priority” option. To the extent permitted by the operating system, run `ntpd` at the highest priority.

Next: ntpd priority, Previous: ntpd nice, Up: ntpd Invocation

#### 1.1.17 pidfile option (-p)

This is the “path to the pid file” option. This option takes a string argument. Specify the name and path of the file used to record `ntpd`’s process ID. This is the same operation as the `pidfile` `pidfile` configuration file directive.

Next: ntpd quit, Previous: ntpd pidfile, Up: ntpd Invocation

#### 1.1.18 priority option (-P)

This is the “process priority” option. This option takes a number argument. To the extent permitted by the operating system, run `ntpd` at the specified `sched_setscheduler(SCHED_FIFO)` priority.

Next: ntpd propagationdelay, Previous: ntpd priority, Up: ntpd Invocation

#### 1.1.19 quit option (-q)

This is the “set the time and quit” option.

This option has some usage constraints. It:

- must not appear in combination with any of the following options: saveconfigquit, wait-sync.

`ntpd` will not daemonize and will exit after the clock is first synchronized. This behavior mimics that of the `ntpdate` program, which will soon be replaced with a shell script. The `-g` and `-x` options can be used with this option. Note: The kernel time discipline is disabled with this option.

Next: ntpd saveconfigquit, Previous: ntpd quit, Up: ntpd Invocation

#### 1.1.20 propagationdelay option (-r)

This is the “broadcast/propagation delay” option. This option takes a string argument. Specify the default propagation delay from the broadcast/multicast server to this client. This is necessary only if the delay cannot be computed automatically by the protocol.

Next: ntpd statsdir, Previous: ntpd propagationdelay, Up: ntpd Invocation

#### 1.1.21 saveconfigquit option

This is the “save parsed configuration and quit” option. This option takes a string argument.

This option has some usage constraints. It:

- must be compiled in by defining `SAVECONFIG` during the compilation.
- must not appear in combination with any of the following options: quit, wait-sync.

Cause `ntpd` to parse its startup configuration file and save an equivalent to the given filename and exit. This option was designed for automated testing.

Next: ntpd trustedkey, Previous: ntpd saveconfigquit, Up: ntpd Invocation

#### 1.1.22 statsdir option (-s)

This is the “statistics file location” option. This option takes a string argument. Specify the directory path for files created by the statistics facility. This is the same operation as the `statsdir` `statsdir` configuration file directive.

Next: ntpd user, Previous: ntpd statsdir, Up: ntpd Invocation

#### 1.1.23 trustedkey option (-t)

This is the “trusted key number” option. This option takes a string argument `tkey`.

This option has some usage constraints. It:

- may appear an unlimited number of times.

Add the specified key number to the trusted key list.

Next: ntpd updateinterval, Previous: ntpd trustedkey, Up: ntpd Invocation

#### 1.1.24 user option (-u)

This is the “run as userid (or userid:groupid)” option. This option takes a string argument.

This option has some usage constraints. It:

- must be compiled in by defining `HAVE_DROPROOT` during the compilation.

Specify a user, and optionally a group, to switch to. This option is only available if the OS supports adjusting the clock without full root privileges. This option is supported under NetBSD (configure with `--enable-clockctl`) or Linux (configure with `--enable-linuxcaps`) or Solaris (configure with `--enable-solarisprivs`).

Next: ntpd wait-sync, Previous: ntpd user, Up: ntpd Invocation

#### 1.1.25 updateinterval option (-U)

This is the “interval in seconds between scans for new or dropped interfaces” option. This option takes a number argument. Give the time in seconds between two scans for new or dropped interfaces. For systems with routing socket support the scans will be performed shortly after the interface change has been detected by the system. Use 0 to disable scanning. 60 seconds is the minimum time between scans.

Next: ntpd slew, Previous: ntpd updateinterval, Up: ntpd Invocation

#### 1.1.26 wait-sync option (-w)

This is the “seconds to wait for first clock sync” option. This option takes a number argument.

This option has some usage constraints. It:

- must be compiled in by defining `HAVE_WORKING_FORK` during the compilation.
- must not appear in combination with any of the following options: nofork, quit, saveconfigquit.

If greater than zero, alters `ntpd`’s behavior when forking to daemonize. Instead of exiting with status 0 immediately after the fork, the parent waits up to the specified number of seconds for the child to first synchronize the clock. The exit status is zero (success) if the clock was synchronized, otherwise it is `ETIMEDOUT`. This provides the option for a script starting `ntpd` to easily wait for the first set of the clock before proceeding.

Next: ntpd usepcc, Previous: ntpd wait-sync, Up: ntpd Invocation

#### 1.1.27 slew option (-x)

This is the “slew up to 600 seconds” option. Normally, the time is slewed if the offset is less than the step threshold, which is 128 ms by default, and stepped if above the threshold. This option sets the threshold to 600 s, which is well within the accuracy window to set the clock manually. Note: Since the slew rate of typical Unix kernels is limited to 0.5 ms/s, each second of adjustment requires an amortization interval of 2000 s. Thus, an adjustment as much as 600 s will take almost 14 days to complete. This option can be used with the `-g` and `-q` options. See the `tinker` configuration file directive for other options. Note: The kernel time discipline is disabled with this option.

Next: ntpd pccfreq, Previous: ntpd slew, Up: ntpd Invocation

#### 1.1.28 usepcc option

This is the “use cpu cycle counter (windows only)” option.

This option has some usage constraints. It:

- must be compiled in by defining `SYS_WINNT` during the compilation.

Attempt to substitute the CPU counter for `QueryPerformanceCounter`. The CPU counter and `QueryPerformanceCounter` are compared, and if they have the same frequency, the CPU counter (RDTSC on x86) is used directly, saving the overhead of a system call.

Next: ntpd mdns, Previous: ntpd usepcc, Up: ntpd Invocation

#### 1.1.29 pccfreq option

This is the “force cpu cycle counter use (windows only)” option. This option takes a string argument.

This option has some usage constraints. It:

- must be compiled in by defining `SYS_WINNT` during the compilation.

Force substitution the CPU counter for `QueryPerformanceCounter`. The CPU counter (RDTSC on x86) is used unconditionally with the given frequency (in Hz).

Next: ntpd config, Previous: ntpd pccfreq, Up: ntpd Invocation

#### 1.1.30 mdns option (-m)

This is the “register with mdns as a ntp server” option.

This option has some usage constraints. It:

- must be compiled in by defining `HAVE_DNSREGISTRATION` during the compilation.

Registers as an NTP server with the local mDNS server which allows the server to be discovered via mDNS client lookup.

Next: ntpd exit status, Previous: ntpd mdns, Up: ntpd Invocation

#### 1.1.31 presetting/configuring ntpd

Any option that is not marked as not presettable may be preset by loading values from environment variables named `NTPD` and `NTPD_<OPTION_NAME>`. `<OPTION_NAME>` must be one of the options listed above in upper case and segmented with underscores. The `NTPD` variable will be tokenized and parsed like the command line. The remaining variables are tested for existence and their values are treated like option arguments.

The command line options relating to configuration and/or usage help are:

#### version (-)

Print the program version to standard out, optionally with licensing information, then exit 0. The optional argument specifies how much licensing detail to provide. The default is to print just the version. The licensing infomation may be selected with an option argument. Only the first letter of the argument is examined:

‘`version`’

  Only print the version. This is the default.

‘`copyright`’

  Name the copyright usage licensing terms.

‘`verbose`’

  Print the full copyright usage licensing terms.

Next: ntpd Usage, Previous: ntpd config, Up: ntpd Invocation

#### 1.1.32 ntpd exit status

One of the following exit values will be returned:

‘`0 (EXIT_SUCCESS)`’

  Successful program execution.

‘`1 (EXIT_FAILURE)`’

  The operation failed or the command syntax was not valid.

Next: ntpd Files, Previous: ntpd exit status, Up: ntpd Invocation

#### 1.1.33 ntpd Usage

Next: ntpd See Also, Previous: ntpd Usage, Up: ntpd Invocation

#### 1.1.34 ntpd Files

Next: ntpd Bugs, Previous: ntpd Files, Up: ntpd Invocation

#### 1.1.35 ntpd See Also

Next: ntpd Notes, Previous: ntpd See Also, Up: ntpd Invocation

#### 1.1.36 ntpd Bugs

Previous: ntpd Bugs, Up: ntpd Invocation

#### 1.1.37 ntpd Notes

Previous: ntpd Invocation, Up: ntpd Description

### 1.2 Usage

What | Default | Flag | Option
--- | --- | --- | ---
configuration file | `/etc/ntp.conf` | `-c` | `conffile`
frequency file | none | `-f` | `driftfile`
leapseconds file | none |  | `leapfile`
process ID file | none | `-p` | `pidfile`
log file | system log | `-l` | `logfile`
include file | none | none | `includefile`
statistics path | `/var/NTP` | `-s` | `statsdir`
keys path | `/usr/local/etc` | `-k` | `keysdir`